.stars {
  overflow: hidden;
  position: absolute;
  width: 100%;
  height: 100%;
  z-index: -1;
  background: radial-gradient(100% 100% at center center, #021, #000);
}

@keyframes flashing {
  0% {
    opacity: 1;
  }
  25% {
    opacity: 0.75;
  }
  50% {
    opacity: 0.5;
  }
  75% {
    opacity: 0.25;
  }
  100% {
    opacity: 0;
  }
}